Lubricating oil composition with reduced phosphorus levels

ABSTRACT

This invention is generally related to a low phosphorus lubricant for an internal combustion engine that provides superior deposit control while still retaining excellent viscosity control.

REFERENCE OF RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 60/665,961 filed Mar. 29, 2005, the disclosure of which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention generally relates to a low phosphorus lubricant for an internal combustion engine that provides superior deposit control while still retaining excellent viscosity control.

BACKGROUND

Future engine oil lubricants will be required to have low levels of phosphorus to protect the emission system, but will also need to provide broad oxidation protection to the lubricant and reduced wear and deposits in the engine. This is a difficult task with existing lubricants because the most effective anti-wear and antioxidant additives are the phosphorus-containing zinc dialkyldithiophosphates (ZDDPs). In the past, high levels of ZDDP were used because ZDDPs were low cost materials and provided superior anti-wear and oxidation performance. However, in the future, ZDDP will only be allowed at low levels. In 2004, some commercial gasoline engine oil specifications allowed a maximum of 800 ppm phosphorus from ZDDP. In future engine oil specifications, levels of phosphorus may drop below 500 ppm, and possibly lower. It is well known that ashless antioxidants can replace some of the oxidation performance lost when levels of ZDDP are reduced. However, it is also known that higher levels of ashless antioxidants do not always lead to improved oxidation control. In fact, modern engine oils generally require the use of two or more ashless antioxidant types in order to compensate for the oxidative stability lost by using less ZDDP. In addition, specifications for deposit control are becoming more demanding. In many cases, modern and future lubricants will require much higher levels of these various ashless antioxidants. Levels of conventional ashless antioxidants in excess of 2.0 wt. % may not be adequate for proper protection of the lubricant and engine. These high levels of conventional ashless antioxidants become costly and may also lead to lubricant deficiencies such as corrosion, rust, and seal incompatibility. New low cost and low ash antioxidant systems are needed that are effective at controlling lubricant oxidation and minimizing engine deposits.

It has been found in this invention that particular combinations and ratios of 4,4′-methylenebis(2,6-di-tert-butylphenol) and alkylated diphenylamines provide unexpectedly superior levels of oxidation and deposit control in low phosphorus engine oils. This allows for the use of significantly lower treat levels of ashless antioxidants. The antioxidant systems of this invention are also effective at significantly reducing the formation of volatile organic molecules that are produced upon heating and oxidation of the lubricant. This effect has significant benefits for the environment, since a reduction in volatile organic molecules should contribute to a reduction in emissions.

SUMMARY OF THE INVENTION

One aspect of the present invention is directed toward a novel lubricating oil composition for an internal combustion engine that provides superior deposit control while still retaining excellent viscosity control. Another aspect of the present invention is directed to the use of the novel lubricating oil composition to reduce the amount of deposits in an internal combustion engine. Yet another aspect of the present invention is directed to the use of the novel lubricating oil composition to reduce the poisoning of the catalyst in an internal combustion engine system.

One composition of the present invention, a low phosphorus engine oil comprises 4,4′methylenebis(2,6-di-tert-butylphenol) and an alkylated diphenylamine; wherein the weight ratio of 4,4′-methylenebis(2,6-di-tert-butylphenol) to the alkylated diphenylamine is greater than or equal to about 0.5 and the engine oil produces less than or equal to 35 mg of total deposits according to a ASTM D7097 measurement.

Another composition of the present invention comprises:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (D) at least one component selected from the group consisting of         dispersants and detergents;     -   (E) zinc dialkyldithiophosphate;

optionally (F) an oil soluble organomolybdenum compound, and

optionally (G) a hindered phenolic antioxidant, with the proviso that the hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol);

wherein the lubricating oil composition contains about 600 ppm or less of phosphorus derived from zinc dialkyldithiophosphate; and

the weight ratio of (B) to (C) is greater than or equal to about 0.5.

Another composition of the present invention comprises:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (E) a zinc dialkyldithiophosphate; and     -   (F) an oil soluble organomolybdenum compound; and

optionally (G) a hindered phenolic antioxidant, with the proviso that the hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol);

wherein:

the weight ratio of (B) to (C) is greater than or equal to about 0.5; and

the composition produces less than or equal to about 35 mg of total deposits according to an ASTM D7097 measurement.

Yet another composition of the present invention comprises:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (D) at least one component selected from the group consisting of         dispersants and detergents;     -   (E) zinc dialkyldithiophosphate;     -   (F) an oil soluble organomolybdenum compound, and     -   (G) a hindered phenolic antioxidant, with the proviso that the         hindered phenolic antioxidant is not         4,4′-methylenebis(2,6-di-tert-butylphenol);

wherein the composition comprises:

about 600 ppm or less of phosphorus derived from zinc dialkyldithiophosphate; and

about 50-400 ppm of molybdenum derived from the oil soluble organomolybdenum compound.

Yet another composition of the present invention is an engine oil lubricating composition comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) 0.2 to 1.0 wt % of an alkylated diphenylamine;     -   (E) 200 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate; and     -   (F) 50 to 400 ppm of molybdenum derived from an oil soluble         organomolybdenum compound;         wherein the weight ratio of (b) to (c) is greater than or equal         to 0.5.

Yet another composition of the present invention is an engine oil lubricating composition comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 0.1 to 1.5 wt % 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (D) 1.0 to 12.0 wt % of at least one compound selected from the         group consisting of dispersants and detergents;     -   (E) 200 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate; and     -   (F) 50 to 400 ppm of molybdenum derived from an oil soluble         organomolybdenum compound;         wherein the weight ratio of (b) to (c) is greater than or equal         to 0.5.

Another composition of the present invention is an engine oil lubricating composition comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) 0.2 to 1.0 wt % of an alkylated diphenylamine, and     -   (D) 300 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate;         wherein the weight ratio of (b) to (c) is greater than or equal         to 0.5.

Yet another composition of the present invention is an engine oil lubricating composition comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 0.1 to 1.5 wt % 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (D) 1.0 to 12.0 wt % of at least one compound selected from the         group consisting of dispersants and detergents, and     -   (E) 300 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate;         wherein the weight ratio of (b) to (c) is greater than or equal         to 0.5.

By “a major amount” it is meant an amount greater than 50 wt % based on the total weight of the composition.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph of the deposit results obtained from ASTM D7097 (TEOST MHT-4) in the absence of MoDTC (molybdenum bis(dialkyldithiocarbamate) containing 4.5 wt. % molybdenum).

FIG. 2 is a graph of the deposit results obtained from ASTM D7097 (TEOST MHT-4) in the presence of MoDTC.

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

ASTM D7097 is the “Standard Test Method for Determination of Moderately High Temperature Piston Deposits by Thermo-oxidation Engine Oil Simulation Tests,” approved December 2004, which is incorporated by reference in its entirety for any purpose. ASTM D7097 is a new standard lubricant industry test for the evaluation of the oxidation and carbonaceous deposit-forming characteristics of engine oils. The test is designed to simulate high temperature deposit formation in the piston ring belt area of modern engines. Details of the test operation and specific conditions for various protocols are further reported in the following publications, all of which are incorporated by reference in their entirety for any purpose:

-   -   Selby and Florkowski, “The Development of the TEOST Protocol MHT         as a Bench Test of Engine Oil Piston Deposit Tendency” in         Proceedings 12th International Colloquium Tribology, TAE,         Ostfildern, Germany, Jan. 11-13, 2000, Supplement, pp 55-62.     -   Selby, Richardson and Florkowski, “Engine Oil Deposits and the         TEOST—Protocol 33 and Beyond” SAE Technical Paper Series,         962039, from International Fall Fuels & Lubricants Meeting and         Exposition, San Antonio, Tex., Oct. 14-17, 1996.     -   Selby, “Recent Developments in Testing Lubricants” 6th         International LFE Congress, Brussels, Belgium, Jun. 2-4, 1999.

The test is also a useful tool for studying the formation of volatile organic molecules upon oxidation of an engine oil. It is generally understood that the formation of volatile organic molecules upon oxidation of a lubricant are detrimental because they lead to an increase in emissions, and can also promote further polymerization of the lubricant. Polymerization of the lubricant leads to viscosity increase, which is also undesirable. The additive combination of this invention is effective at controlling both deposit formation and the formation of volatile organic molecules. Typically, polar volatile organic molecules are formed by decomposition of an organic peroxide in the lubricant. This decomposition produces an organic alkoxy radical that can react with another oil molecule to produce an alcohol, or that can degrade to form aldehydes and ketones. The degradation to aldehydes and ketones generally reduces molecular weight and thus produces more volatile fragments, which are pollutants and are also active precursors to oligomers and polymers that thicken the lubricant. It is therefore highly desirable to prevent or eliminate the formation of these polar volatile organic molecules.

A “low phosphorus engine oil,” as used herein, refers to an engine oil that contains less than about 600 ppm of phosphorus derived from zinc dialkyldithiophosphate.

“Hydrocarbyl” as used herein refers to any alkyl, alkenyl, or alkynyl group, which can be linear, cyclic or any combination thereof, wherein each group is optionally substituted. Such substituents may include reactive groups, including but not limited to succinic groups.

The term “about” as used herein means including and exceeding up to 20% the specific endpoint(s) designated. Thus the range is broadened, for example “about 1” is intended to include the range 0.8 to 1.2.

Organic friction modifiers are molecules containing long non-polar hydrocarbon chains possessing a polar end-group that has affinity for the metal engine surface. An “organic friction modifier,” as used herein includes but is not limited to long chain organic fatty or carboxylic acids, esters, ethers, amines, imides, amides, sulfurized fatty acids, metallo-organic compounds, high molecular weight organic phosphorus and phosphoric acid esters. Examples of other conventional organic friction modifiers are described in R. Hoogendoorn and D. Kenbeek, “Friction Modifiers to the Rescue” in Lubes-n-Greases (2003), Vol. 9, Issue 11, pp. 14-20, which is incorporated by reference in its entirety for any purpose. Organic friction modifiers are typically used between 0 and 1.0 wt. % in fully formulated engine oils.

A “corrosion inhibitor” as used herein includes but is not limited to thiadiazole polysulfides containing from 5 to 50 carbon atoms, their derivatives and polymers thereof. Typical corrosion inhibitors are disclosed in Hamblin, et al., “Ashless Antioxidants, Copper Deactivators and Corrosion Inhibitors: their Use in Lubricating Oils” Lubrication Science (1990), 2(4), pp. 287-318. Suitable corrosion inhibitors include derivatives of 1,3,4 thiadiazoles such as polysulfide derivatives of 2,5-dimercapto-1,3,4-thiadiazole (1,3,4-thiadiazole polysulfide) having the general formula:

wherein R¹ and R² are the same or different hydrocarbon radicals and can be aliphatic or aromatic, including alkyl, aralkyl, aryl and alkaryl radicals, x and y are 0 to about 8, the sum of x and y is at least 1, and in some embodiments between 2 and 16. Methods of preparing such compounds are disclosed in U.S. Patent Nos. 2,719,125, 2,719,126, and 3,087,932 which are each incorporated by reference in its entirety for any purpose. Other similar materials are described in U.S. Patent Nos. 3,821,236; 3,904,537; 4,097,387; 4,107,059; 4,136,043; 4,188,299; and 4,193,882. Other corrosion inhibitors are the thio and polythio sulfenamides of thiadiazoles such as those of the general formulae:

wherein z is from 2 to 5 and R³ is hydrogen, a hydrocarbyl group, another sulphenamide or thiosulphenamide group, R⁴ and R⁵ can be hydrogen or hydrogen and carbon containing groups, provided R⁴ and R⁵ are not both hydrogen or R⁴ and R⁵ form a heterocyclic ring with the nitrogen to which they are attached, as described in UK Patent Specification No. 1,560,830. All of the cited references are incorporated by reference herein in their entirety for any purpose. Benzotriazoles derivatives also fall within this class of additives. Other examples of corrosion inhibitors include dodecenyl succinic acids, esters, amides, and mixed ester/amides, fatty amines, linear alkyl amines, fatty acids, linear carboxylic acids, some branched alkyl amines, some branched carboxylic acids, sulfur and phosphorus compounds and some detergents. Corrosion inhibitors are typically used between 0 and 0.5 wt. % in a fully formulated engine oil.

A “viscosity modifier,” as used herein includes those modifiers which function to impart high and low temperature operability to a lubricating oil. Such modifiers include, but are not limited to polyisobutylene, copolymers of ethylene and propylene and higher alpha-olefins, polymethacrylates, polyalkylmethacrylates, methacrylate copolymers, copolymers of an unsaturated dicarboxylic acid and a vinyl compound, inter polymers of styrene and acrylic esters, and partially hydrogenated copolymers of styrene/isoprene, styrene/butadiene, and isoprene/butadiene, as well as the partially hydrogenated homopolymers of butadiene and isoprene and isoprene/divinylbenzene. Typical viscosity modifiers are polymers having a molecular weight ranging from 20,000 to 1,000,000. Typical viscosity modifiers are disclosed in M. K. Mishra and R. G. Saxton, “Polymer Additives For Engine Oils” CHEMTECH, April 1995, pp. 35-41, which is incorporated by reference herein for any purpose.

Pour point depressants are molecules that are added to an oil that interfere with and alter wax crystal growth at low temperatures. A “pour point depressant,” as used herein includes those depressants which function to lower the minimum temperature at which the fluid will flow or can be poured. Such depressants include, but are not limited to C₈ to C₁₈ dialkyl fumarate/vinyl acetate copolymers, polyalkylmethacrylates and the like. Typical pour point depressants are disclosed in Mishra and Saxton, CHEMTECH, April 1995, pp. 35-41.

A “phosphorus-free anti-wear additive,” as used herein refers to any phosphorus-free compound that reduces wear in an engine, an engine test, or a bench wear test, when added to a fully formulated engine oil. Examples of phosphorus-free anti-wear additives include sulfurized olefins, sulfurized fatty acids and oils, sulfurized fatty esters, sulfurized mixed fatty acid/fatty esters, sulfurized mixed fatty acid/olefins, sulfurized mixed fatty esters/fatty acids, organic sulfides, disulfides, trisulfides and polysulfides, thiocarbamates, thiuram sulfides, disulfides, trisulfides and polysulfides, molybdenum dithiocarbamates, zinc dithiocarbamates, molybdenum amine complexes, molybdenum alcohol complexes, mixed molybdenum amine/molybdenum alcohol complexes, and molybdenum carboxylates.

A “fully formulated engine oil” as used herein may contain additional, typical additives known to those skilled in the industry, and is used as an engine oil in an as-received basis.

II. Components of the Invention

Component (A)

Component (A) may be any combination of an oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks. Component (A) may further include up to about 15% by weight of a Group I basestock. The various basestock groups are identified chemically and physically in the American Petroleum Institute (API) publication Engine Oil Licensing and Certification System, Industry Services Department, 14^(th) Ed. (December 1996) Addendum 1 (December 1998), which is hereby incorporated by reference in its entirety for any purpose. In one embodiment of the invention, the base stock has a viscosity of 3-12 mm²/s (cSt) at 100° C.; in another embodiment, the base stock has a viscosity of 4-10 mm²/s (cSt) at 100° C.; and in yet another embodiment, the base stock has a viscosity of 4.5-8 mm²/s (cSt) at 100° C.

Group II mineral oil base stocks contain greater than or equal to 90 wt % saturates and less than or equal to 0.03 wt % sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table 1 below. In one embodiment, Group II basestocks contain greater than or equal to 95 wt % saturates and less than or equal to 0.01 wt % sulfur and have a viscosity index greater than or equal to 100 and less than 120 using the test methods specified in Table 1 below.

Group III mineral oil base stocks contain greater than or equal to 90 wt % saturates and less than or equal to 0.03 wt % sulfur and have a viscosity index greater than or equal to 120 using the test methods specified in Table 1 below. In one embodiment, Group III basestocks contain greater than or equal to 98 wt % saturates and less than or equal to 0.01 wt % sulfur and have a viscosity index greater than or equal to 130 using the test methods specified in Table 1 below.

Group IV base stocks are poly-α-olefins.

Suitable ester base stocks that can be used include the esters of dicarboxylic acids (e.g. phthalic acid, succinic acid, alkyl succinic acids, alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g. butyl alcohol, hexyl alcohol, dodecyl alcohol 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol, etc.). Specific examples of these esters include dibutyl adipate, bis(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, di-isooctyl azelate, di-isodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid and the like.

Esters useful as base stock oils also include those made from C₅-C₁₂ monocarboxylic acids and polyols and polyol ethers, such as neopentyl glycol, trimethylol propane, pentaerythritol, dipentaerythritol, tripentaerythritol, etc. TABLE 1 Analytical Methods for Testing Base Stocks Property Test Method Saturates ASTM D2007 Viscosity Index ASTM D2270 Sulfur ASTM D2622, D4292, D4927 or D3120

Component A comprises from about 75 to 97 wt % of the composition based on the total weight of the composition. Most preferably Component A will comprise from about 80 to 95 wt %.

Component (B)

The chemical structure of 4,4′-methylenebis(2,6-di-tert-butylphenol), a hindered phenolic antioxidant, is depicted below:

In one embodiment of the invention, 4,4′-methylenebis(2,6-di-tert-butylphenol) is used between about 0.1 and about 1.5 wt. % in a fully formulated engine oil.

Component (C)

Alkylated diphenylamine (component C) has the general formula: R_(a)—NH—R_(b), wherein R_(a) and R_(b) each independently represents a substituted or unsubstituted phenyl group. Substituents on the phenyl rings may include but are not limited to alkyl groups having from 1 to 20 carbon atoms, alkylaryl groups, hydroxy, carboxy and nitro groups. In one embodiment of the invention, one or both of the phenyl groups are substituted with an alkyl. In yet another embodiment of the invention, both phenyl groups are alkyl substituted.

Examples of alkylated diphenylamines which can be used in the present invention include 3-hydroxydiphenylamine, N-phenyl-1,2-phenylenediamine, N-phenyl-1,4-phenylenediamine, butyldiphenylamine, dibutyldiphenylamine, octyldiphenylamine, dioctyldiphenylamine, nonyldiphenylamine, dinonyldiphenylamine, heptyldiphenylamine, diheptyldiphenylamine, methylstyryldiphenylamine, mixed butyl/octyl alkylated diphenylamines, mixed butyl/styryl alkylated diphenylamines, mixed ethyl/nonyl alkylated diphenylamines, mixed octyl/styryl alkylated diphenylamines, mixed ethyl/methylstyryl alkylated diphenylamines, and combinations of these of varying degrees of purity that are commonly used in the petroleum industry.

In one embodiment of the invention, the nitrogen content of the alkylated diphenylamines ranges from about 2 wt % to about 12 wt % of the alkylated diphenylamine. The concentration of the alkylated diphenylamine in the fully formulated oil can vary depending on customers' requirements and applications, and the desired level of antioxidant protection required for the specific composition of this invention. In one embodiment of the invention, the alkylated diphenylamines are present in the compositions of this invention in an amount from about 0.05 wt % to about 1.0 wt % of the composition weight; in another embodiment in an amount from about 0.1 wt % to about 0.75 wt %; in yet another embodiment, the alkylated diphenylamines are present in an amount from about 0.2 wt % to about 1.0 wt %.

Component (D)

The composition further comprises any dispersant and/or detergent (component D) used in engine oils and known in the art. In one embodiment of the invention either a detergent or dispersant is present in the fully formulated engine oil formulation. In another embodiment, both a detergent and a dispersant are present in the fully formulated engine oil formulation. Either the dispersant or the detergent may be boronated, or borated.

Dispersants are well known in the field of lubricants and include primarily what are sometimes referred to as “ashless” dispersants because (prior to mixing in a lubricating composition) they do not contain ash-forming metals and they do not normally contribute any ash-forming metals when added to a lubricant.

Dispersants typically are nonmetallic additives containing nitrogen or oxygen polar groups attached to a high molecular weight hydrocarbon chain. The hydrocarbon chain provides solubility in the hydrocarbon base stocks. The dispersants function to keep oil degradation products suspended in the oil. Examples of suitable dispersants include but are not limited to polymethacrylates, styrene-maleic ester copolymers, substituted succinimides (e.g., PIBSA (polyisobutylene succinic anhydride)), polyamine succinimides, polyhydroxy succinic esters, substituted Mannich bases, and substituted triazoles.

The dispersants may be borated. Borated dispersants are well-known materials and can be prepared by treatment with a borating agent such as boric acid. Typical conditions include heating the dispersant with boric acid at about 100 to 150° C. The dispersants may also be treated by reaction with maleic anhydride; for example, a succinimide dispersant can be prepared by the reaction of an amount of an α,β,-unsaturated acid or equivalent thereof, such as maleic anhydride, with an amount of an amine with a hydrocarbyl-substituted acylating agent characterized by the presence of at least 1.3 succinic groups for each equivalent weight of substituent group, wherein the reaction of the acid can be simultaneous with or subsequent to the reaction of the amine and the hydrocarbyl-substituted acylating agent, as described in WO 00/26327, filed Oct. 13, 1999, which is incorporated herein by reference in its entirety for any purpose.

In one embodiment of the invention, the amount of dispersant in the composition of this invention range from about 0.5 wt. % to about 10 wt. % based on the total composition weight. In another embodiment of the invention, the amount of dispersant in the compositions of the invention range from about 1.0 wt. % to about 12.0 wt. %; in yet another embodiment the amount ranges from about 1.0 wt. % to about 8.0 wt. %. In another embodiment of the invention, the amount of dispersant in the composition of this invention range from about 3.0 wt. % to about 7.0 wt. %. Its concentration in a concentrate will be correspondingly increased to, e.g., from about 5 wt. % to about 90 wt. %.

Detergents are generally salts of organic acids, which are often overbased. Metal overbased salts of organic acids are widely known to those of skill in the art and generally include metal salts wherein the amount of metal present exceeds the stoichiometric amount. Detergents are typically metallic additives containing metal ions and polar groups, such as sulfonates or carboxylates, with aliphatic, cycloaliphatic or alkylaromatic chains. The detergents function by lifting deposits from the various surfaces of the engine. Suitable detergents include neutral and overbased alkali and alkaline earth metal sulfonates, neutral and overbased alkali and alkaline earth metal phenates, sulfuirized phenates, and overbased alkaline earth salicylates. Patents describing techniques for making detergents generally include U.S. Pat. Nos. 2,501,731; 2,616,905; 2,616,911; 2,616,925; 2,777,874; 3,256,186; 3,384,585; 3,365,396; 3,320,162; 3,318,809; 3,488,284; and 3,629,109, all of which are hereby incorporated by reference for any purpose.

The detergents generally can be borated by treatment with a borating agent such as boric acid. Typical conditions include heating the detergent with boric acid at about 100 to 150° C., the number of equivalents of boric acid being roughly equal to the number of equivalents of metal in the salt. U.S. Pat. No. 3,929,650 discloses borated complexes prepared by contacting boric acid with an alkali metal carbonate overbased metal sulfonate (prepared by overbasing a neutral alkali or alkaline earth metal sulfonate with an alkali metal carbonate) in an oleophilic liquid reaction medium and is incorporated herein by reference in its entirety for any purpose.

In one embodiment of the invention, the amount of detergent in a composition of this invention ranges from about 0.5 wt. % to about 5 wt. % based on the total weight of the composition. In another embodiment of the invention, the amount of detergent in a composition of the invention ranges from about 1.0 wt. % to about 6.0 wt. %; in yet another embodiment, the amount ranges from about 1.0 wt. % to about 4.0 wt. %. In another embodiment of the invention, the amount of detergent in a composition of this invention ranges from about 1.0 wt. % to about 3.0 wt. %. Its concentration in a concentrate will be correspondingly increased, to, e.g., about 5 wt. % to about 70 wt. %.

Component (E)

The zinc dialkyldithiophosphate (ZDDP) (component E) in the oil composition may be any ZDDP derived from the reaction of an alcohol or phenol and phosphorus pentasulfide (P₂S₅) to produce a dialkyldithiophosphoric acid derivative (DDPA) followed by neutralization with a basic zinc compound.

Zinc salts (M=Zn) of the formula:

wherein R⁸ and R⁹ are independently hydrocarbyl groups containing 3 to 30 carbon atoms are readily obtainable by the reaction of (P₂S₅) and an alcohol or phenol to form an O,O-dihydrocarbyl phosphorodithioic acid of the formula:

The reaction involves mixing at a temperature of 20° C. to 200° C., four moles of an alcohol or a phenol with one mole of phosphorus pentasulfide. Hydrogen sulfide is liberated in this reaction. The acid is then reacted with a basic zinc compound to form the salt. In one embodiment of the invention, the basic zinc compound is zinc oxide (ZnO) and the resulting zinc compound is represented by the formula:

The R⁸ and R⁹ groups are independently hydrocarbyl groups that are, in one embodiment of the invention, free from acetylenic unsaturation. In another embodiment, R⁸ and R⁹ are free from ethylenic unsaturation and in yet another embodiment, R⁸ and R⁹ are free from both acetylenic and ethylenic unsaturation. In one embodiment, R⁸ and R⁹ are alkyl, cycloalkyl, aralkyl or alkaryl groups and have 3 to 20 carbon atoms; in another embodiment they have 3 to 16 carbon atoms and in yet another embodiment up to 13 carbon atoms, e.g., 3 to 13 carbon atoms. The alcohols which react to provide the R⁸ and R⁹ groups can be one or more primary alcohols, one or more secondary alcohols, or a mixture of secondary alcohol and primary alcohol. A mixture of two secondary alcohols such as isopropanol and 4-methyl-2-pentanol also can be used.

Such materials are often referred to as zinc dialkyldithiophosphates or simply zinc dithiophosphates. They are well known and readily available to those skilled in the art of lubricant forrnulation.

In one embodiment of the invention, the level of ZDDP delivers less than about 600 ppm of phosphorus to the compositions of this invention; in one embodiment between about 200 and about 600 ppm of phosphorus is delivered; in yet another embodiment, between about 300 and about 600 ppm is delivered. The “ppm” is based on the total weight of the composition. In another embodiment, the level of ZDDP delivers less than about 550 ppm of phosphorus to the compositions of this invention. For example, a ZDDP containing 8.5 wt. % phosphorus would be used at a level less than 0.65 wt. % in the compositions of this invention. In yet another embodiment, the level of ZDDP delivers less than about 500 ppm of phosphorus to the compositions of this invention.

Component (F)

Any oil soluble organomolybdenum compound (component F) may be used as an optional component in the lubricating compositions of the present invention. The quantity of molybdenum delivered to the compositions of this invention will vary depending upon the customers' requirements and applications, and the desired level of antioxidant protection required for the specific composition of this invention. Any concentration of oil soluble organomolybdenum may be used, but in one embodiment, the level is less than about 600 ppm. In another embodiment, the level is less than about 500 ppm. In yet another embodiment, the level is about 50-400 ppm. In another embodiment, the molybdenum level is about 100-250 ppm. In yet another embodiment, the level of molybdenum metal is about 250-400 ppm. The “ppm” is based on the total weight of the composition.

In general, molybdenum is an effective antioxidant in lubricating oil compositions; however, the use of molybdenum in the compositions of this invention need to be balanced against the cost of oil soluble organomolybdenum compounds compared to other antioxidants, such as ZDDP.

Examples of some oil soluble organomolybdenum compounds that may be used in this invention include molybdenum dithiocarbamates, oxymolybdenum sulfide dithiocarbamates, molybdenum dithioxanthogenates, oxymolybdenum sulfide dithioxanthogenates, molybdenum organophosphorodithioates, oxymolybdenum sulfide organophosphorodithioates, molybdenum carboxylates, molybdenum amine complexes, molybdenum alcohol complexes, molybdenum amide complexes, mixed molybdenum amine/alcohol/amide complexes, and combinations of these. In one embodiment of the invention the molybdenum compound is a sulfur-containing and phosphorus-free compound.

Component (G)

Component (G) may be any hindered phenolic antioxidant other than 4,4′-methylenebis(2,6-di-tert-butylphenol). Component (G) may be for example: 2,6-di-tert-butylphenol; 2,6-di-tert-butyl-4-methylphenol; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, isooctyl ester; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, C₇-C₉-branched alkyl esters; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, n-octadecyl ester; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, n-butyl ester; 2,4,6-tri-tert-butylphenol; 2,4-di-tert-butylphenol; 4,4′-thiobis(2,6-di-tert-butylphenol); 4,4′-dithiobis(2,6-di-tert-butylphenol); 4,4′-polythiobis(2,6-di-tert-butylphenol); 2,2′-thiobis(4,6-di-tert-butylphenol); 2,2′-dithiobis(4,6-di-tert-butylphenol); 2,2′-polythiobis(4,6-di-tert-butylphenol); 4,4′-ethylidenebis(2,6-di-tert-butylphenol); 4,4′-butylidenebis(2,6-di-tert-butylphenol); 2,2′-methylenebis(4,6-di-tert-butylphenol); 2,2′-ethylidenebis(4,6-di-tert-butylphenol); 2,2′-butylidenebis(4,6-di-tert-butylphenol); 4,4′-thiobis(2-methyl-6-tert-butylphenol); 4,4′-dithiobis(2-methyl-6-tert-butylphenol); 4,4′-polythiobis(2-methyl-6-tert-butylphenol); 2,2′-thiobis(4-methyl-6-tert-butylphenol); 2,2′-dithiobis(4-methyl-6-tert-butylphenol); 2,2′-polythiobis(4-methyl-6-tert-butylphenol); 4,4′-ethylidenebis(2-methyl-6-tert-butylphenol); 4,4′-butylidenebis(2-methyl-6-tert-butylphenol); 2,2′-methylenebis(4-methyl-6-tert-butylphenol); 2,2′-ethylidenebis(4-methyl-6-tert-butylphenol); 2,2′-butylidenebis(4-methyl-6-tert-butylphenol); 4,4′-methylenebis(2-methyl-6-tert-butylphenol); octylphenol; nonylphenol; dodecylphenol; thiobis(octylphenol); thiobis(nonylphenol); thiobis(dodecylphenol); dithiobis(octylphenol); dithiobis(nonylphenol); dithiobis(dodecylphenol); polythiobis(octylphenol); polythiobis(nonylphenol); polythiobis(dodecylphenol); methylenebis(octylphenol); methylenebis(nonylphenol); methylenebis(dodecylphenol); ethylidenebis(octylphenol); ethylidenebis(nonylphenol); ethylidenebis(dodecylphenol); butylidenebis(octylphenol); butylidenebis(nonylphenol); butylidenebis(dodecylphenol); α,α′-thiobis(2,6-di-tert-butyl-p-cresol); α,α′-thiobis(2-methyl-6-tert-butyl-p-cresol); 2,6-di-tert-butyl-4-ethylphenol; 2,6-di-tert-butyl-4-butylphenol; 2,6-di-tert-butyl-4-octylphenol 2,6-di-tert-butyl-4-isoheptylphenol; 2,6-di-tert-butyl-4-isooctylphenol; 2,6-di-tert-butyl-4-(2-ethylhexyl)phenol; 2,6-di-tert-butyl-4-isononylphenol; 2,6-di-tert-butyl-4-nonylphenol 2,6-di-tert-butyl-4-isodecylphenol; 2,6-di-tert-butyl-4-isododecylphenol; 2,6-di-tert-butyl-4-dodecylphenol; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, isoheptyl ester; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, isononyl ester; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, isodecyl ester; 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, isododecyl ester; or non-volatile multi-ring (or methylene bridged) tert-butylphenolics as defined below:

where X can vary from 1 to 5, and R is hydrogen or tert-butyl, or as defined in any one of U.S. Pat. No. 3,211,652, wherein for example, R can be a hydrogen or an alkyl group having from 4 to about 9 carbon atoms, U.S. Patent Application 2002/0142923, and U.S. Pat. No. 2,807,653, wherein for example, R can be hydrogen or a hydrocarbon radical containing up to about 9 carbon atoms. Each of the cited references is hereby incorporated by reference in its entirety for any purpose.

In one embodiment of the invention, the hindered phenolic antioxidant contains sulfur. In another embodiment of the invention, the hindered phenolic antioxidant is sulfur-free.

In one embodiment of the invention, the amount of hindered phenolic antioxidant other than 4,4′-methylenebis(2,6-di-tert-butylphenol) is present in the composition of this invention in an amount between about 0.1 wt. % and about 0.75 wt. %; in another embodiment it is present in an amount between about 0.1 wt. % and about 0.5 wt. %, all wt % being based on the total weight of the composition.

III. OTHER EMBODIMENTS OF THE INVENTION

This invention provides a lubricating oil composition capable of providing improved deposit control to an internal combustion engine.

In one aspect of the invention, a low phosphorus engine oil composition comprises: 4,4′-methylenebis(2,6-di-tert-butylphenol) and an alkylated diphenylamine; wherein the weight ratio of 4,4′-methylenebis(2,6-di-tert-butylphenol) to the alkylated diphenylamine is greater than or equal to about 0.5 and the engine oil produces less than or equal to 35 mg of total deposits according to a ASTM D7097 measurement. In one embodiment, the composition further comprises a zinc dialkyldithiophosphate; wherein the engine oil comprises about 600 ppm or less of phosphorus derived from the zinc dialkyldithiophosphate. In another embodiment, the composition further comprises an oil soluble organomolybdenum compound. Engine oils include formulated oils used in gasoline, diesel, natural gas and railroad engines.

In one aspect of the invention, the engine oil comprises:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (D) at least one component selected from the group consisting of         dispersants and detergents; and     -   (E) a zinc dialkyldithiophosphate (ZDDP);         wherein the composition comprises about 600 ppm or less of         phosphorus derived from zinc dialkyldithiophosphate (ZDDP); and         the weight ratio of (B) to (C) is greater than or equal to about         0.5.

In another embodiment of the invention the composition further comprises an oil soluble organomolybdenum compound. In yet another embodiment, the oil soluble organomolybdenum compound comprises sulfur and is phosphorus-free. In one embodiment of the invention, the weight ratio of phosphorus to molybdenum in the composition is greater than or equal to 1.0. In another embodiment, the weight ratio of phosphorus to molybdenum is greater than 0.0 and less than 1.0. In yet another embodiment of the invention, the weight ratio of phosphorus to molybdenum is less than or equal to 1.0. In another embodiment of the invention, the compositions can contain (G) a hindered phenolic antioxidant, with the proviso that the hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol). In another embodiment of the invention, the sum of (B), (C) and (G) is less than or equal to about 1.5 wt. % of the composition. In another embodiment of the invention, the oil of lubricating viscosity (component (A)) comprises up to about 15% by weight (based on the weight of component A) of a Group I baseoil. A further embodiment is a lubricating oil composition described above, wherein the composition produces less than or equal to about 35 mg of total deposits according to an ASTM D7097 measurement; in another embodiment, the composition produces less than or equal to about 25 mg of total deposits according to an ASTM D7097 measurement; and in yet another embodiment, the composition produces less than or equal to about 15 mg of total deposits.

In another aspect of the invention, the engine oil comprises:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol); and     -   (C) an alkylated diphenylamine;     -   (E) a zinc dialkyldithiophosphate; and     -   (F) an oil soluble organomolybdenum compound;         wherein the weight ratio of (B) to (C) is greater than or equal         to about 0.5; and the composition produces less than or equal to         about 35 mg of total deposits according to an ASTM D7097         measurement.

In one embodiment of the invention, the oil soluble organomolybdenum compound comprises sulfur and is phosphorus-free. In one embodiment, the weight ratio of phosphorus to molybdenum is greater than or equal to 1.0; in another embodiment the weight ratio is greater than 0.0 and less than 1.0. In yet another embodiment of the invention, the weight ratio of phosphorus to molybdenum is less than or equal to 1.0. In another embodiment of the invention, the composition further comprises at least one component selected from the group consisting of dispersants and detergents. In another embodiment of the invention, the engine oil further comprises (G) a hindered phenolic antioxidant, with the proviso that the hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol). In yet another embodiment, the sum of (B), (C) and (G) is less than or equal to about 1.5 wt. % of the composition. In a further embodiment of the invention, such compositions produce less than or equal to about 25 mg of total deposits according to an ASTM D7097 measurement. In yet another embodiment of the invention, the engine oil further comprises (D) at least one component selected from the group consisting of dispersants and detergents and (G) a hindered phenolic antioxidant, with the proviso that the hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol). In yet another embodiment, the sum of (B), (C) and (G) is less than or equal to about 1.5 wt. % of the engine oil. In a further embodiment of the invention, this engine oil produces less than or equal to about 25 mg of total deposits according to an ASTM D7097 measurement. A further embodiment is an engine oil described above, wherein the engine oil produces less than or equal to 15 mg of total deposits according to an ASTM D7097 measurement.

In yet another aspect of the invention, the engine oil comprises:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol); and     -   (C) an alkylated diphenylamine;     -   (D) a zinc dialkyldithiophosphate;     -   (E) an oil soluble organomolybdenum compound;     -   (F) at least one component selected from the group consisting of         dispersants and detergents; and     -   (G) a hindered phenolic antioxidant, with the proviso that the         hindered phenolic antioxidant is not         4,4′-methylenebis(2,6-di-tert-butylphenol);         wherein the composition comprises: about 600 ppm or less of         phosphorus derived from zinc dialkyldithiophosphate and about         50-400 ppm of molybdenum derived from the oil soluble         organomolybdenum compound.

In one embodiment of the invention, the oil soluble organomolybdenum compound comprises sulfur and is phosphorus-free. In one embodiment, the weight ratio of phosphorus to molybdenum is greater than or equal to 1.0; in another embodiment the weight ratio is greater than 0.0 and less than 1.0. In yet another embodiment of the invention, the weight ratio of phosphorus to molybdenum is less than or equal to 1.0. In another embodiment of the invention, the engine oil comprises about 550 ppm or less of phosphorus derived from the zinc dialkyldithiophosphate. In another embodiment of the invention, the engine oil comprises about 500 ppm or less of phosphorus derived from the zinc dialkyldithiophosphate. In yet another embodiment of the invention, the composition comprises about 400 ppm or less of phosphorus derived from the zinc dialkyldithiophosphate. In yet another embodiment, the engine oil comprises about 300 ppm or less of phosphorus derived from the zinc dialkyldithiophosphate. In another embodiment of the invention, the engine oil comprises about 100-250 ppm of molybdenum derived from the oil soluble organomolybdenum compound. In yet another embodiment of the invention, the engine oil comprises about 250-400 ppm of molybdenum derived from the oil soluble organomolybdenum compound. In yet another embodiment of the invention, the engine oil comprises about 300-400 ppm of molybdenum derived from the oil soluble organomolybdenum compound. In yet another embodiment of the invention, the composition comprises about 50-150 ppm of molybdenum derived from the oil soluble organomolybdenum compound. All parts per million (ppm) in this paragraph are based on the total weight of the engine oil

Yet another aspect of the invention is an engine oil comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) 0.2 to 1.0 wt % of an alkylated diphenylamine;     -   (E) 200 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate; and     -   (F) 50 to 400 ppm of molybdenum derived from an oil soluble         organomolybdenum compound;         wherein the weight ratio of (B) to (C) is greater than or equal         to 0.5.

Yet another aspect of the invention is an engine oil lubricating composition comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 0.1 to 1.5 wt % 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (D) 1.0 to 12.0 wt % of at least one compound selected from the         group consisting of dispersants and detergents;     -   (E) 200 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate; and     -   (F) 50 to 400 ppm of molybdenum derived from an oil soluble         organomolybdenum compound;         wherein the weight ratio of (B) to (C) is greater than or equal         to 0.5.

In one embodiment of the invention the engine oil comprises 0.1 to 0.5 wt % of any ester derived from 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid.

Another aspect of the invention is an engine oil comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) 0.2 to 1.0 wt % of an alkylated diphenylamine, and     -   (E) 300 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate;         wherein the weight ratio of (B) to (C) is greater than or equal         to 0.5.

In one embodiment of the invention the engine oil further comprises 0.1 to 0.5 wt % of any ester derived from 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid.

Another aspect of the invention is an engine oil comprising:

-   -   (A) a major amount of oil of lubricating viscosity selected from         the group consisting of Group II, Group III, Group IV and         synthetic ester base stocks;     -   (B) 0.1 to 1.5 wt % 4,4′-methylenebis(2,6-di-tert-butylphenol);     -   (C) an alkylated diphenylamine;     -   (D) 1.0 to 12.0 wt % of at least one compound selected from the         group consisting of dispersants and detergents, and     -   (E) 300 to 600 ppm of phosphorus derived from zinc         dialkyldithiophosphate; wherein the weight ratio of (B) to (C)         is greater than or equal to 0.5.

All weight percents (wt %) given above for the engine oils of this invention are based on the total weight of the engine oil. By “a major amount” it is meant an amount greater than 50 wt % based on the total weight of the engine oil.

An additional embodiment of this invention is any composition or engine oil described above further comprising one or more components selected from the group consisting of an organic friction modifier, a corrosion inhibitor, a viscosity modifier, a pour point depressant, and a phosphorus-free anti-wear additive.

A further aspect of this invention is a method of reducing the amount of total volatile organics (both polar and non-polar in nature) produced by an internal combustion engine upon heating and oxidation of an engine oil, comprising lubricating the engine with any composition or engine oil described herein.

Yet another aspect of this invention is a method of reducing the amount of deposits in an internal combustion engine comprising lubricating the engine with any composition or engine oil described herein.

A further aspect of this invention is a method of reducing the poisoning of the catalyst in an internal combustion engine emission system, comprising lubricating the engine with any composition or engine oil described herein.

The following combinations are examples of embodiments of the invention, in which the sum of (B), (C) and (G) is less than or equal to about 1.5 wt. % of the composition. Combination I. Component Wt. % B 4,4′-methylenebis(2,6-di-tert-butylphenol) 0.7 C nonylated diphenylamine 0.4 G 2,6-di-tert-butylphenol 0.3

Combination II. Component Wt. % B 4,4′-methylenebis(2,6-di-tert-butylphenol) 0.6 C nonylated diphenylamine 0.4 G 3,5-di-tert-butyl-4-hydroxyhydrocinnamic 0.4 acid, isooctyl ester

The TEOST MHT instrument should be run according to the ASTM D7097 method and manufacturer specifications. The test involves passing a thin film of test engine oil over a heated wire-wound depositor rod with the aide of a precision pump. The test rod is heated at 285° C. and the test run for 24 hours. The thin film of oil moves evenly down the rod and is collected at the flow out point of the test assembly apparatus. Recovered oil is circulated back to the depositor rod via the precision pump. During the 24 hour test period volatiles are produced that flash off the hot rod surface and condense on the glass mantle of the test assembly apparatus. These volatiles are recovered at the volatiles out port of the test assembly and are collected in a glass vial. At the end of the test, deposits are determined by the increase in depositor rod weight and reported in milligrams (mg). The collected volatiles are accurately weighed and reported in grams (g).

The method requires a number of independent calibrations, including for example, calibrating the air flow rate, the oil pump rate, the temperature controller settings, and the control thermocouple. The method also requires running certified reference oils periodically to determine the severity of the test. For example, a certified medium deposit reference oil should produce approximately 40-60 mg of deposits, while a certified high deposit reference oil should produce approximately 70-90 mg of deposits. It is understood that a severe test condition will usually produce heavier deposits and higher levels of volatiles. On the other hand, a mild test condition will usually produce lighter deposits and much lower levels of volatiles. Engine oils that perform well, i.e. low deposits and low volatiles, under a severe test condition are expected to perform even better under a mild test condition. However, engine oils that perform well under a mild test condition are expected to perform worse under a severe test condition. The additive combination of this invention gives excellent deposit control and reduced volatiles formation under both severe and mild conditions. The robust performance of the new additive combination under both severe and mild test conditions is another advantage of this invention.

III. EXAMPLES

Measurement of Deposits and Volatiles in TEOST-MHT

The fully formulated oil (8.4 g) and an organometallic catalyst (about 0.1 g) are added to a flask equipped with a Teflon stirring bar and stirred for 20-60 minutes without heating. The depositor rod, sample flask, oil inlet, air inlet, and volatiles collection vial are fitted to the TEOST apparatus according to manufacturers specifications. The pump is started at a high flow rate and run until the test oil reaches the connection of the pump and oil feed tube, at which point the pump flow is turned to zero. The heater switch is turned on and when the depositor rod temperature controller is between 200-210° C., the pump speed increased to achieve a sample delivery of 0.25±0.02 g/min, making sure that the oil is flowing down the depositor rod and is not leaking. The temperature is allowed to stabilize at 285±2° C. and the test is run under these conditions for 24 hrs.

Three test tubes are prepared with cyclohexane or another suitable hydrocarbon solvent for extraction of oil from the depositor rod. The test instrument is disassembled as per manufacturer's instructions and the depositor rod is transferred to a weighing boat and kept under cover. The depositor rod is placed successively for 10 minutes each in each of the three test tubes prepared with a hydrocarbon solvent. The rod is placed in tared weighing boat and allowed to sit for 10 minutes to insure evaporation of the hydrocarbon solvent. The rod and the boat are weighed, verifying that a constant mass has been achieved. The contents of the three test tubes, along with the lower-end cap deposits and glass mantle deposits, are washed into a common container which is then filtered using a glass funnel equipped with a filter cartridge. After completing the filtering, the filter cartridge is dried under vacuum and weighed, until a constant mass is achieved. The total mass of the deposits from the depositor rod and filter deposits is then determined.

During the 24 hour duration of the test, the volatile compounds in the formulated oil that are there originally or those formed during the test, are flashed off the depositor rod. These volatiles condense on the glass mantle and are collected on a continuous basis in a small, weighed vial. The vial and volatiles are measured at the end of the 24 hour test period and the amount of volatiles is calculated by subtracting the original weight of the vial.

Example A

A preblend was prepared by blending the following materials:

-   -   150N Group II Baseoil, 92.1 wt. %;     -   an ashless dispersant concentrate, 4.92 wt. %;     -   an overbased detergent concentrate containing calcium, 1.85 wt.         %;     -   a neutral detergent concentrate containing calcium, 0.51 wt. %;         and     -   a secondary zinc dialkyldithiophosphate, 0.62 wt.

To this preblend was added the following components as indicated in Table 2 in preparation of a variety of engine oils. The finished engine oil contained the following (calculated): calcium 2400 ppm; phosphorus 470 ppm; zinc 520 ppm; and had a total base number of 7.5 mg KOH/g of oil.

The finished oils were tested in the TEOST MHT according to ASTM D7097. The certified medium deposit reference oil produced 60.6 mg of deposits in a calibration experiment. The certified high deposit reference oil produced 96.8 mg of deposits in a calibration experiment; these results represent a severe condition for the TEOST MHT instrument. The results of the analysis under severe conditions are reported in Table 2. TABLE 2 Composition and Total Deposits for Examples A.1-A.17 from ASTM D7097 Total Total Ex. MoDTC Mo SO NDPA HPE MBBP MBDTBP Volatiles Deposits No. (g) (ppm) (g) (g) (g) (g) (g) (g)* (mg)* A.1 Comparative 1.00 1.00 44 A.2 Comparative 1.50 3.2 50 2.8 46 A.3 Comparative 0.75 2.7 55 A.4 Comparative 0.80 360 0.75 2.8 50 A.5 Comparative 0.80 360 1.50 3.1 25 2.5 31 A.6 Comparative 0.75 0.40 2.5 39 2.7 41 A.7 Comparative 0.75 0.75 3.0 41 A.8 Comparative 0.75 0.40 2.4 33 2.4 46 A.9 Comparative 0.75 0.75 2.7 29 A.10 Invention 0.75 0.40 3.2 44 A.11 Invention 0.75 0.75 2.3 14 A.12 Comparative 0.80 360 0.75 0.40 2.5 29 2.4 28 A.13 Comparative 0.80 360 0.75 0.75 2.2 26 2.6 28 A.14 Comparative 0.80 360 0.75 0.40 3.1 35 A.15 Comparative 0.80 360 0.75 0.75 2.6 19 A.16 Invention 0.80 360 0.75 0.40 2.2 32 A.17 Invention 0.80 360 0.75 0.75 2.2 12 1.9 10 MoDTC = Molybdenum bis(dialkyldithiocarbamate) containing 4.5 wt. % molybdenum SO = Sulfurized Olefin containing 12 wt. % sulfur NDPA = Nonylated diphenylamine HPE = 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, C₇-C₉-branched alkyl esters MBBP = Non-volatile multi-ring (or methylene bridged) tert-butylphenolics MBDTBP = 4,4′-methylenebis(2,6-di-tert-butylphenol) *more than one result indicates a duplicated run

Table 2 clearly shows that the combination of MBDTBP, NDPA and MoDTC in the invention leads to low levels of deposits (12 and 10 mg) and volatiles (2.2 and 1.9 g) in the TEOST MHT using ASTM D7097. It is also clear that the combination of MBDTBP and NDPA without MoDTC in the invention leads to low levels of deposits (14 mg) and volatiles (2.3 g) in the TEOST MHT using ASTM D7097.

A graph of the deposit results in the presence of MoDTC is shown in FIG. 1.

A graph of the deposit results in the absence of MoDTC is shown in FIG. 2.

Example B Oil Thickening and Oxidation at Elevated Temperatures

A preblend was prepared by blending the following materials:

-   -   4.92 wt. % of an ashless dispersant concentrate;     -   1.85 wt. % of an overbased detergent concentrate containing         calcium;     -   0.51 wt. % of a neutral detergent concentrate containing         calcium;     -   0.62 wt. % of a secondary zinc dialkyldithiophosphate; and     -   92.10 wt. % of a 150N Group II baseoil.

To this engine oil preblehd was added the components indicated in Table 3. TABLE 3 Components of Examples B.1-B.6. Engine Oil Ex. Preblend HPE NDPA ZDDP MoN SO MBDTBP G2BO Total No. Example Type (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) B.1 Comparative 97.50 0.75 0.75 1.00 100.00 B.2 Comparative 97.50 0.75 0.75 0.29 0.71 100.00 B.3 Comparative 97.50 0.75 0.75 0.50 0.50 100.00 B.4 Comparative 97.50 0.75 0.75 1.00 100.00 B.5 Comparative 97.50 0.75 0.75 0.25 0.50 0.25 100.00 B.6 Invention 97.50 0.75 0.50 0.40 0.85 100.00 MoN = A nitrogen-containing organomolybdenum compound containing 7.2 wt. % molybdenum G2BO = 150 N Group II baseoil

These finished engine oils contained the following elements and physical properties (calculated): For examples B.1, B.3, B.4, B.5, and B.6: calcium 2400 ppm; phosphorus 470 ppm; zinc 520 ppm; and a total base number (TBN) of 8.6 mg KOH/g of oil. For example B.2: calcium 2400 ppm; phosphorus 690 ppm; zinc 765 ppm; and a total base number of 8.6 mg KOH/g of oil.

The oxidative stability of these finished engine oils was evaluated in a bulk oil oxidation test. Each oil (300 mL) was treated with an iron naphthenate oxidation catalyst to deliver 110 ppm of iron to the finished oil. The oils were heated in a block heater at 160° C., while 10 liters/hour of dry oxygen was bubbled through the oil. Samples of the oxidized oils were removed at 24, 48, 72 and 96 hours. Kinematic viscosities of each sample were determined at 40° C. The percent viscosity increase of the oxidized oil versus the fresh oil was calculated. The percent viscosity increase results are shown in Table 4. TABLE 4 Percent viscosity increase of finished oils B.1-B.6 in bulk oil oxidation test. Time Ex. B.1 Ex. B.2 Ex. B.3 Ex. B.4 Ex. B.5 Ex. B.6 (hrs) Comparative Comparative Comparative Comparative Comparative Invention 24  75.6  35.6 3.8 31.6 3.7 2.3 48 328.3 165.2 6.0 116.2 26 4.2 72 TVTM 466.3 111.6 287.7 225.4 31.0 96 TVTM TVTM 952.7 338.7 TVTM 256.3 TVTM = too viscous to measure

A higher percent viscosity increase is a measure of increased oxidation and degradation of the lubricant. The designation TVTM is an indication of severe degradation of the lubricant. These results clearly show that the inventive antioxidant combination in Example B.6 provides superior oxidation protection compared to the other Examples (B.1-B.5). Antioxidant systems that do not contain the organomolybdenum component (B.1, B.2 and B.4) show poor oxidation control, while the system containing the hindered phenolic MBDTBP (B.6) is superior to the system containing the hindered phenolic HPE (B.3).

Example C Oil Thickening and Oxidation

Oils A.2, A.3, A.7, A.9, A.11, A.13, A.15, A.16, and A.17 (Table 2) were evaluated in the bulk oil oxidation test described in Example B. In this study the oils were heated in a heating block at 150° C., while 10 liters/hour of dry oxygen was bubbled through the oil. Samples of the oxidized oils were removed at 24, 48, 72 and 96 hours. Kinematic viscosities of each sample were determined at 40° C. The percent viscosity increase of the oxidized oil versus the fresh oil was calculated. The percent viscosity increase results are shown in Table 5. TABLE 5 Percent viscosity increase of oils A.2, A.3, A.7, A.9, and A.11 in bulk oil oxidation test. Time Oil A.2 Oil A.3 Oil A.7 Oil A.9 Oil A.11 Oil A.13 Oil A.15 Oil A.16 Oil A.17 (hrs) Compar. Compar. Compar. Compar. Inventive Compar. Compar. Inventive Inventive 24 2 0 10 0 1 n/a n/a n/a n/a 48 51 112 151 48 52 2.1 0.7 0 1.6 72 193 313 429 201 207 3.0 1.9 0.7 3.3 96 461 753 1129 535 526 2.8 2.0 1.5 −0.3 n/a = not measured

These results show that Oil A.11 is comparable to Oils A.2 and A.9, and significantly better than Oils A.3 and A.7. However, Oil A.11 also shows a significant improvement in deposit control and volatiles relative to all the oils, as was demonstrated in Example A. Therefore, the Inventive Oil A.11 is an overall better performing engine oil, providing excellent viscosity control, deposit control, and control of volatile organic compounds. The ability of the inventive Oil A.11 to show benefits in all these parameters is of value. Antioxidant systems that contain the organomolybdenum compound (A.13, A.15, A.16 and A.17) show superior viscosity control.

The foregoing examples are not limiting and are merely illustrative of various aspects and embodiments of the present invention. All documents cited herein are indicative of the levels of skill in the art to which the invention pertains and are incorporated by reference herein in their entireties for any purpose. None, however, is admitted to be prior art.

One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The methods and compositions described illustrate a variety of embodiments, are exemplary, and are not intended as limitations on the scope of the invention. Certain modifications and other uses will occur to those skilled in the art and are encompassed within the spirit of the invention, as defined by the scope of the claims.

The invention illustratively described herein may be suitably practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in of the use of such terms and expressions of excluding any equivalents of the features shown and described, or portions thereof. It is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by described embodiments, optional features, modification and variations of the concepts herein disclosed may be resorted to by those skilled in the art and such modifications and variations are considered to be within the scope of this invention as defined by the description and the appended claims. 

1. A low phosphorus engine oil comprising: 4,4′-methylenebis(2,6-di-tert-butylphenol) and an alkylated diphenylamine; wherein the weight ratio of 4,4′-methylenebis(2,6-di-tert-butylphenol) to said alkylated diphenylamine is greater than or equal to about 0.5; and said engine oil produces less than or equal to 35 mg of total deposits according to a ASTM D7097 measurement.
 2. An engine oil according to claim 1, further comprising a zinc dialkyldithiophosphate; wherein said engine oil comprises about 600 ppm or less of phosphorus derived from said zinc dialkyldithiophosphate.
 3. An engine oil according to claim 2, further comprising an oil soluble organomolybdenum compound.
 4. A composition comprising: (a) a major amount of oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks; (b) 4,4′-methylenebis(2,6-di-tert-butylphenol); (c) an alkylated diphenylamine; (d) at least one component selected from the group consisting of dispersants and detergents; and (e) a zinc dialkyldithiophosphate; wherein said composition comprises about 600 ppm or less of phosphorus derived from said zinc dialkyldithiophosphate; and the weight ratio of (b) to (c) is greater than or equal to about 0.5.
 5. A composition according to claim 4, further comprising (f) an oil soluble organomolybdenum compound.
 6. A composition according to claim 5, wherein said oil soluble organomolybdenum compound comprises sulfur and is phosphorus-free.
 7. A composition according to claim 6, wherein the weight ratio of phosphorus to molybdenum is greater than or equal to 1.0.
 8. A composition according to claim 6, wherein the weight ratio of phosphorus to molybdenum is greater than 0.0 and less than 1.0.
 9. A composition according to claim 6, wherein the weight ratio of phosphorus to molybdenum is less than or equal to 1.0.
 10. A composition according to claim 4 further comprising: (g) a hindered phenolic antioxidant with the proviso that said hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol).
 11. A composition according to claim 10 wherein the sum of (b), (c) and (g) is less than or equal to about 1.5 wt. % of said composition.
 12. A composition according to claim 6 further comprising (g) a hindered phenolic antioxidant with the proviso that said hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol).
 13. A composition according to claim 12 wherein the sum of (b), (c) and (g) is less than or equal to about 1.5 wt. % of said composition.
 14. A composition according to claim 4 wherein said oil of lubricating viscosity comprises up to about 15% by weight of a Group I baseoil.
 15. A composition comprising: (a) a major amount of oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks; (b) 4,4′-methylenebis(2,6-di-tert-butylphenol); (c) an alkylated diphenylamine; (e) a zinc dialkyldithiophosphate; and (f) an oil soluble organomolybdenum compound; wherein: the weight ratio of (b) to (c) is greater than or equal to about 0.5; and said composition produces less than or equal to about 35 mg of total deposits according to a ASTM D7097 measurement.
 16. A composition according to claim 15 wherein said oil soluble organomolybdenum compound comprises sulfur and is phosphorus-free.
 17. A composition according to claim 15, wherein the weight ratio of phosphorus to molybdenum is greater than or equal to 1.0.
 18. A composition according to claim 15, wherein the weight ratio of phosphorus to molybdenum is greater than 0.0 and less than 1.0.
 19. A composition according to claim 15, wherein the weight ratio of phosphorus to molybdenum is less than or equal to 1.0.
 20. A composition according to claim 15 further comprising: (d) at least one component selected from the group consisting of dispersants and detergents.
 21. A composition according to claim 15 further comprising: (g) a hindered phenolic antioxidant with the proviso that said hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol).
 22. A composition according to claim 21 wherein the sum of (b), (c) and (g) is less than or equal to about 1.5 wt. % of said composition.
 23. A composition according to claim 21 wherein said composition produces less than or equal to about 25 mg of total deposits according to an ASTM D7097 measurement.
 24. A composition according to claim 20 further comprising (g) a hindered phenolic antioxidant with the proviso that said phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol).
 25. A composition according to claim 24 wherein the sum of (b), (c) and (g) is less than or equal to about 1.5 wt. % of said composition.
 26. A composition according to claim 24 wherein said composition produces less than or equal to about 25 mg of total deposits according to an ASTM D7097 measurement.
 27. A composition comprising: (a) a major amount of oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks; (b) 4,4′-methylenebis(2,6-di-tert-butylphenol); and (c) an alkylated diphenylamine; (d) at least one component selected from the group consisting of dispersants and detergents; (e) a zinc dialkyldithiophosphate; (f) an oil soluble organomolybdenum compound; and (g) a hindered phenolic antioxidant with the proviso that said hindered phenolic antioxidant is not 4,4′-methylenebis(2,6-di-tert-butylphenol); wherein said composition comprises: about 600 ppm or less of phosphorus derived from said zinc dialkyldithiophosphate; and about 50-400 ppm of molybdenum derived from said oil soluble organomolybdenum compound.
 28. A composition according to claim 27, wherein said oil soluble organomolybdenum compound comprises sulfur and is phosphorus-free.
 29. A composition according to claim 27, wherein the weight ratio of phosphorus to molybdenum is greater than or equal to 1.0.
 30. A composition according to claim 27, wherein the weight ratio of phosphorus to molybdenum is greater than 0.0 and less than 1.0.
 31. A composition according to claim 27, wherein the weight ratio of phosphorus to molybdenum is less than or equal to 1.0.
 32. A composition according to claim 27 wherein said composition comprises about 550 ppm or less of phosphorus derived from said zinc dialkyldithiophosphate.
 33. A composition according to claim 27 wherein said composition comprises about 100-250 ppm of molybdenum derived from said oil soluble organomolybdenum compound.
 34. A composition according to claim 27 wherein said composition comprises about 500 ppm or less of phosphorus derived from said zinc dialkyldithiophosphate.
 35. A composition according to claim 27 wherein said composition comprises about 250-400 ppm of molybdenum derived from said oil soluble organomolybdenum compound.
 36. An engine oil comprising: (a) a major amount of oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks; (b) 4,4′-methylenebis(2,6-di-tert-butylphenol); (c) 0.2 to 1.0 wt % of an alkylated diphenylamine; (d) 1.0 to 12.0 wt % of at least one compound selected from the group consisting of dispersants and detergents; (e) 200 to 600 ppm of phosphorus derived from zinc dialkyldithiophosphate; and (f) 50 to 400 ppm of molybdenum derived from an oil soluble organomolybdenum compound; wherein the weight ratio of (b) to (c) is greater than or equal to 0.5.
 37. An engine oil comprising: (a) a major amount of oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks; (b) 0.1 to 1.5 wt % 4,4′-methylenebis(2,6-di-tert-butylphenol); (c) an alkylated diphenylamine; (d) 1.0 to 12.0 wt % of at least one compound selected from the group consisting of dispersants and detergents; (e) 200 to 600 ppm of phosphorus derived from zinc dialkyldithiophosphate; and (f) 50 to 400 ppm of molybdenum derived from an oil soluble organomolybdenum compound; wherein the weight ratio of (b) to (c) is greater than or equal to 0.5.
 38. An engine oil according to claim 37 further comprising: (g) 0.1 to 0.5 wt % of any ester derived from 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid.
 39. An engine oil comprising: (a) a major amount of oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks; (b) 4,4′-methylenebis(2,6-di-tert-butylphenol); (c) 0.2 to 1.0 wt % of an alkylated diphenylamine, and (d) 1.0 to 12.0 wt % of at least one compound selected from the group consisting of dispersants and detergents, and (e) 300 to 600 ppm of phosphorus derived from zinc dialkyldithiophosphate; wherein the weight ratio of (b) to (c) is greater than or equal to 0.5.
 40. An engine oil according to claim 39 further comprising: (g) 0.1 to 0.5 wt % of any ester derived from 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid.
 41. An engine oil comprising: (a) a major amount of oil of lubricating viscosity selected from the group consisting of Group II, Group III, Group IV and synthetic ester base stocks; (b) 0.1 to 1.5 wt % 4,4′-methylenebis(2,6-di-tert-butylphenol); (c) an alkylated diphenylamine; (d) 1.0 to 12.0 wt % of at least one compound selected from the group consisting of dispersants and detergents, and (e) 300 to 600 ppm of phosphorus derived from zinc dialkyldithiophosphate; wherein the weight ratio of (b) to (c) is greater than or equal to 0.5.
 42. A method of reducing the amount of total volatile organics produced by an internal combustion engine upon heating and oxidation of an engine oil comprising lubricating said engine with a composition according to claim
 1. 43. A method of reducing the amount of deposits in an internal combustion engine, comprising lubricating said engine with a composition according to claim
 1. 44. A method of reducing the poisoning of the catalyst in an internal combustion engine emission system comprising lubricating said engine with a composition according to claim
 1. 